Friday, February 15, 2013

East Asian Small Breasts Linked to 35,000-Year-Old DNA Mutation

The traits — thicker hair shafts, more sweat glands, characteristically
identified teeth and smaller breasts — are the result of a gene mutation
that occurred about 35,000 years ago, the researchers have concluded.

The discovery explains a crucial juncture in the evolution of East
Asians. But the method can also be applied to some 400 other sites on
the human genome. The DNA changes at these sites, researchers believe,
mark the turning points in recent human evolution as the populations on
each continent diverged from one another.

The first of those sites to be studied contains the gene known as EDAR.
Africans and Europeans carry the standard version of the gene, but in
most East Asians, one of the DNA units has mutated.
Mice already have EDAR, an ancient mammalian gene that plays a leading
role in the embryo in shaping hair, skin and teeth. The Broad team
engineered a strain of mice whose EDAR gene had the same DNA change as
the East Asian version of EDAR. When the mice grew up, the researchers found they did indeed have
thicker hair shafts, confirming that the changed gene was the cause of
East Asians’ thicker hair.

A series of selections on different traits thus made the variant version
so common among East Asians. About 93 percent of Han Chinese carry the
variant, as do about 70 percent of people in Japan and Thailand, and 60
to 90 percent of American Indians, a population descended from East
Asians.